Percutaneous Transvascular Arterial Bypass
Atherosclerosis is a progressive disease process in which the flow within the lumen of an artery becomes restricted by a blockage, typically referred to as an athersclerotic plaque. In the heart, as well as the periphery, a blockage of an artery can result in pain, disfunction and even death. Numerous methods have been employed over the years to revascularize the tissue downstream of an arterial blockage. These methods include bypass grafting--using artificial, in-situ venous, or transplanted venous grafts, as well as angioplasty, atherectomy and most recently, laser transmyocardial revascularization. Bypass grafting has been extremely successful; however, the procedure requires extensive surgery. Recently, newer techniques such as the transthoracic endoscopic procedure being pursued by the company, Heartport, Inc. and Cardiothoracic Systems, Inc., illustrate the need for a less invasive method of bypassing coronary vessels. These procedures are very difficult to perform, and may not be widely applicable. While transmyocardial laser revascularization, a technique in which small holes are drilled through the wall of the heart, looks promising, the method of action is not yet well understood, and problems exist with the use of laser energy to create the channels. Yet clinicians are still very interested in the technique because is has the potential to be minimally invasive, and does not require the patient to be placed on cardiopulmonary bypass.
In the 1970s several cardiovascular surgeons experimented with the use of cardiac veins for revascularization. The procedure was for use on patients which had severely diffuse stenotic coronary vessels. The technique involved using an intervening graft from the internal mammary artery or an aortic attachment to a saphenous vein. Instead of sewing the grafts to the distal coronary artery, the grafts were attached to the coronary or cardiac vein in the same location. The proximal portion of the vein was then ligated to prevent a shunt, and the patient was then taken off cardiopulmonary bypass, and chest was closed. In this model, the vein were `arterialized`, allowing flow in a retrograde fashion in a effort to bring oxygenated blood to the venules and capillaries of the heart. The success of this technique varied greatly, and was for the most part abandoned. Problems included stenosis at the anastomosis, intracardiac hemorrhages from ruptured venules, and thrombosis of the grafts.
The devices, systems and methods proposed in this disclosure suggest a new method of percutaneous revascularization. Here, the cardiac veins may either be arterialized, or may be simply used as bypass grafts. There is no literature to suggest that this has been ever been attempted. While in-situ bypass grafts have been made in the periphery, still an incision is made to attach and ligate the vein ends. Another procedure which bears some resemblance to this technique is called the TIPS procedure--transjugular intrahepatic portosystemic shunt. In this procedure a stent is advanced into liver tissue to connect the portal vein to the inferior vena cava. While this procedure can be accomplished percutaneously, it is not for the purpose of revascularization of an organ or to bypass a blockage within a vessel, does not permit retrograde flow within either of the two vessels, is not performed with an accompanying embolization, and requires the use of a stent. Further, the devices and methods used in that setting are too large and do not have the directional capability necessary for use in smaller vessels such as those found in the heart.
Transvascular Intervascular Interstitial Surgery
Open surgery was for many years the only way to gain access to tissues to perform a surgical maneuver. With the advent of optics, various endoscopic procedures were developed. Initially, these procedures utilized natural orifices such as the urinary tract, oral cavity, nasal canal and anus. Most recently, new techniques using transabdominal and transthoracic ports have been developed. These thorascopic or laparoscopic procedures essentially use instruments which are long-shafted versions of their counterparts in open surgery. General anesthesia is usually required, and there are still several smaller wounds which require healing.
Another problem that exists with this approach is the identification of anatomically consistent reference points. For precise surgery, such as in the brain, a frame is usually attached to the patients head to provide this reference. More recently, a `frameless` system has been developed which utilizes a much smaller frame mounted with several light emitting diodes (LEDs). The LEDs are correlated to LEDs on the instrument itself using three cameras mounted to the ceiling. This aid in the correlation of the frame to the landmarks, and assures proper positioning of the instrument. While this seems like an extensive effort, it underlines the importance of gaining access to the exact location desired.
Traditionally, the vascular system has been entered for the sole purpose of addressing a vascular problem. Angioplasty, atherectomy, stents, laser angioplasty, thrombolysis and even intracardiac biopsy devices have all been designed for intravascular use.